Theme 1C Flashcards by Zunaira Ali

What is semiconservative replication

Each daughter strand is paired with its complimentary parent strand

Blue red

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What is conservative replication

Both daughter strands pair up together and parent strands pair together

Red red blue blue

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What is dispersive replication

Daughter strands have a mix of parental and newly made dna

Mix of blue and red throughout whole dna

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What is the Meselson and stahl experiment

They put nitrogen isotopes N15, N14 into the DNA molecule through the nitrogenous bases.

They spun the N 15 solution and found that it appeared as a single N15 band.

Then they transferred it to the N14 solution and replicated it, DNA showed a single band intermediate between the N15 and N14 isotope.

They replicated it again in the N14 medium and it showed as two bands, one in the intermediate between N15 and N14, and the other only in the N14 position. This means there were some hybrid daughter/parent strand dna, and some only new daughter dna

Experiment showed that ecoli was semiconservative replication

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What direction does DNA replication occur? Why

5’-3’
Nucleotides can only be added to the 3’ OH end of the strand

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How is the new dna backbone able to be formed during replication

The hydrolysis of phosphate provides energy for the formation of the phosphodiester bond.

It’s does this by cleaving off two phosphates out of three, and these two phosphates (pyrophosphate) provide energy.

The other phosphate stays in the daughter strand backbone

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What direction does the dna polymerase read the parent strand during replication

3-5

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What does DNA polymerase need to make a new daughter strand

An RNA primer to kickstart synthesis

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What is a replisome

The molecule machine of enzymes that replicates DNA

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What is helicase

Unwinds the double helix by braking the hydrogen bonds

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What is primase

The enzyme that makes RNA primers for DNA pol to start replicating

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What is the single stranded binding protien

The protien that attaches to single stranded DNA before replication

stabilizes (prevents reannealing) so it can act as template

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What is DNA topoisomerase/gyrase

The enzyme that relaxes dna and prevents coils/ tangles from forming ahead of the replication fork

Relives torque

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What is DNA pol III

Makes the new daughter strand by adding nucleotides to the new DNA strand/rna primer

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What is DNA pol I

It remove the RNA primer and fill the gap made by the removal with dna (dNTPs)

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What is the sliding clamp

Attaches DNA POL III to template strand so replication is faster/efficient

What is DNA ligase

Fill in the gaps of the lagging strand by forming phosopdiester bonds

Because DNA pol I cant seal the ends of DNA segments

Where does replication occur on the dna?

Why is there a leading and lagging strand

At the replication forks

Because dna can only be made in 5-3, if one parent strand is in the 5-3 direction, the dna pol needs to work backwards in small fragments (lagging stand) to stay anitparallel

What are the steps of DNA replication in order

DNA helicase
RNA primase
Topoisomerase
DNA POL III
DNA POL I
DNA ligase

What are the steps of dna replication in bacterial chromosomes? (Prokaryotes)

Intitiation
Elongation
Termination

What is the initiation step in replicating bacterial DNA

Unwinding and separation of the two template DNA strands at the origin of replication. This forms a replication bubble with two forks.

What is the elongation step in replicating DNA in bacteria

Simultaneous synthesis of the two DNA strands from the template strands by DNA polymerase

What is the termination step of DNA replication in bacteria

replication stops when it reaches a termination site (for circular prokaryotes)

or the end of the chromosome (for linear)

What bases are likely to be found at the origin of replication

A and T because hydrogen bonds are easier to break

Easier to unwind and start replication

What’s different between Linear and circular dna replication, why

Linear has multiple origins of replication, so that replication can be completed on time during s phase. because it is a much bigger genome.

Explain the process of DNA replication in a test tube (PCR)

You denature the DNA (95) so that it comes apart Primer anneal: primer on the strands to begin replication (50-60 degrees). raise the temperature (72) so that DNA polymerase can replicate best and extend the strand. Then repeat for 30 cycles

What is the problem with replicating the ends of linear chromosomes? What is the result of this

When rna primer at the very end of the strand is removed, the DNA pol can’t fill it in because it would have to synthesize from the 5’ end (which it can’t do) This causes a loss of the chromosomal ends after every round of cell division/dna replication Can lead to death of the organism bc genes at the end of strand are deleted

What is a solution to the end replication problem

Telomerase adds a telomere (non-coding, single-stranded DNA) to the 3’ end of the template strand, the telomeres will be worn away after each replication not the actual DNA Once telomeres are gone, cell stops dividing

What is telomerase

Enzyme that restores shortened telomeres Present in gametes and stem cells (gives newborn cells long telomeres)

What is cengenics

Company testing the length of your telomeres and giving supplements to elongate them

How does cancer relate to telomeres

Cancers get mutations that activate the telomerase gene to stop the limitations of rapid cell division. This cause an excess of cell division, which is the cause of cancer

What is anti cancer therapeutics

Telomerase, inhibitors or telomerase vaccine that activates the immune system to kill cancer cells that express the telomerase gene

What is the proof reading process of DNA POL

When base pair mistake occurs DNA Pol III backtracks and removes the most recent mismatched nucleotide through exonuclease activity. After mistake is removed, it replaces with the correct nucleotide and resumes synthesis. This process has to happen fast and it can’t happen if polymerase goes too far after the mistake

Why does DNA mismatch repair happen?

Happens if there are replication errors that aren’t corrected by proofreading

What do MUTS and MUTL do?

Recognize the mismatch damage and call over MUTH to fix

What does MUTH do

It’s an endonuclease, which nicks the daughter strand several nucleotides away from the mismatch

What does EXO1 do

Travel in opposite direction on daughter strand where MUTH had cut and cuts out the mismatch and the region around it

What does dna pol III and ligase do in mismatch repair

Fills the gap left by EXO1 and repairs mismatch. Ligase fills in the nicks left behind